fix: correct ASSERT_EQ to ASSERT_NE in admittance controller load test (backport #2264)

[mergify]

Fixes #1258

Problem

The test_load_controller test in admittance_controller was using ASSERT_EQ to check against nullptr, which means the test was asserting that the controller fails to load. Since the controller loads successfully with the params file provided, the test was always passing, even though it was checking the wrong condition.

Fix

Changed ASSERT_EQ to ASSERT_NE so the test correctly asserts that the controller loaded successfully (i.e. the result is not nullptr).

Note: range_sensor_broadcaster already has the correct ASSERT_NE in its load test and does not need changes.

Is this user-facing behavior change?

no

Did you use Generative AI?

no

---

This is an automatic backport of pull request #2264 done by Mergify.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.77%. Comparing base (c2a182f) to head (5a5b74d).
⚠️ Report is 1 commits behind head on kilted.

Additional details and impacted files

@@           Coverage Diff           @@
##           kilted    #2339   +/-   ##
=======================================
  Coverage   85.77%   85.77%           
=======================================
  Files         152      152           
  Lines       15082    15082           
  Branches     1293     1293           
=======================================
  Hits        12936    12936           
  Misses       1688     1688           
  Partials      458      458           

Flag	Coverage Δ
unittests	85.77% <ø> (ø)

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Files with missing lines	Coverage Δ
...ontroller/test/test_load_admittance_controller.cpp	100.00% <ø> (ø)

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